Quantum computing is an emerging technology that leverages a quantum mechanical phenomenon not available in classical systems (e.g., superposition and entanglement, etc.) to process information. In a conventional computing system, the basic unit of information is a bit, which is a two-state element that can be in either a “one” or a “zero” state. In contrast, the basic unit of information in a quantum-computing system, referred to as a qubit, can be in any superposition of both states at the same time (referred to as “superposition states”). Furthermore, many qubits can be in a superposition of correlated states in a way that the system cannot be described as a product of the individual qubit states (referred to as “entangled states”). These forms of qubit states representing the information are not available in conventional (classical) computers. As a result, theoretically, a large-scale quantum computer can solve some problems that simply are not practically feasible using conventional computing approaches. Unfortunately, quantum computers have proven difficult to realize in large scale due.
One attractive avenue for realizing practical quantum computing is “trapped-ion processing,” in which atomic ions are trapped in a free-space position via a quadrupole ion trap (a.k.a. an RF Paul Trap). The position of the trap location is determined by the RF field null in the electric field generated by the RF signals applied to a plurality of RF driver electrodes that define the ion trap. Once trapped, the ions are addressed and read-out optically using one or more optical signals.
Ideally, collection of entangled photons emitted form a trapped ion would be done via photonic interconnects monolithically integrated with the ion trap itself, where the photonic interconnects could then be optically coupled with conventional single-mode optical fibers. This would enable a pair of atomic ion qubits to be entangled in two remote locations and create distributed entangled states for a quantum network. By distributing entangled qubit pairs over several individual quantum processing units, the limitation on the total number of trapped ions that can be combined into a single processing unit could be overcome.
Unfortunately, the integration of optical elements (e.g., mirrors, lenses, optical fibers, photonic interconnects, etc.), with ion traps having highly accurate ion positioning capability has proven challenging. The development of ion traps integrated with small-volume optical cavities, however, has led to improved system performance due to a more efficient photon collection platform that improves entanglement generation rates between remote ions and faster quantum state detection.
For example, the trap location within an optical-cavity-based ion trap is precisely positioned at an antinode of the cavity mode in order to maximize the coupling strength between the ion and the cavity. The trap location is characterized by a vanishing of the radio frequency (RF) field, called the RF null, which is determined by the geometry of the RF electrodes. For a linear surface trap, for example, the height of the trapping location above the substrate (i.e., trap height) is determined by the spacing and width of its linear RF electrodes. Unfortunately, fabrication tolerances during fabrication of the ion trap limits the precision with which an antinode can be located, thereby giving rise to errors in antinode position that degrade ion-trap performance from its theoretical maximum.
Furthermore, ion motion synchronous with the varying amplitude of the RF-based electric field can give rise to “micromotion” of a trapped ion. Unfortunately, micromotion can lead to positional shifts in trap location that are several orders of magnitude larger than desirable, thereby reducing the efficiency of photon collection from an ion trap. Mitigation of micromotion by establishing a static electric field via an arrangement of DC electrodes added to the ion trap has been demonstrated in the prior art. Such micromotion compensation ensures that the ion sits at the null of the RF field formed due to the RF voltages by adjusting DC voltages applied at the DC electrodes to push the ions to the exact RF null. Typically, the generated static electric field is kept constant to avoid perturbations that can push the ion to an area with finite RF fields, thereby leading to micromotion.
An ion trap having three-dimensional control over the position of its trapping location without causing micromotion would be a significant advance in the state of the art of quantum computing and quantum communications.